Belt-type continuous stepless speed changer

ABSTRACT

A belt-type continuously variable transmission ( 15 ) includes a primary sheave ( 29 ) having a pair of first clamp surfaces ( 37   a   , 37   b ), a secondary sheave ( 30 ) having a pair of second clamp surfaces ( 51   a   , 51   b ), and a belt ( 31 ) endlessly wound between both the sheaves ( 29, 30 ). The belt ( 31 ) has contact surfaces ( 58   a   , 58   b ) clamped between the first clamp surfaces ( 37   a   , 37   b ) and between the second clamp surfaces ( 51   a   , 51   b ). Powder ( 64 ) having infusibility as a friction enhancing material is held on at least one of the first clamp surfaces ( 37   a   , 37   b ) of the primary sheave ( 29 ), the second clamp surfaces ( 51   a   , 51   b ) of the secondary sheave ( 30 ), and the contact surfaces ( 58   a   , 58   b ) of the belt ( 31 ).

TECHNICAL FIELD

The present invention relates to a belt-type continuously variabletransmission that transmits a torque of a primary sheave to a secondarysheave via an endless belt, and a sheave and a belt that are used inthis continuously variable transmission, and more particularly to astructure for preventing slip of the belt at an initial stage ofdriving. Further, the invention relates to a vehicle such as amotorcycle mounted with the belt-type continuously variabletransmission.

BACKGROUND ART

JP-A-2002-147553, for instance, discloses a belt-type continuouslyvariable transmission for motorcycles, which can steplessly adjust atransmission gear ratio according to a condition of running. Thisbelt-type continuously variable transmission includes a primary sheave,a secondary sheave, and a belt.

The primary sheave is driven by power transmission from an engine. Theprimary sheave has a pair of clamp surfaces opposed to each other and abelt groove formed between these clamp surfaces. The secondary sheave isinterlocked with a rear wheel of the motorcycle via a reductionmechanism. This secondary sheave has a pair of clamp surfaces opposed toeach other and a belt groove formed between these clamp surfaces.

The belt is endlessly wound between the belt groove of the primarysheave and the belt groove of the secondary sheave. The belt has contactsurfaces for contact with the clamp surfaces of the respective sheaves.Torque of the primary sheave is transmitted to the secondary sheave viathe belt by frictional force generated between the contact surfaces ofthe belt and the clamp surfaces of the respective sheaves.

As is shown in FIG. 18, this kind of belt-type continuously variabletransmission has a characteristic that, as thrust, which causes theclamp surfaces of the respective sheaves to clamp the belt, increases,the torque transmissible between the sheaves and the belt increasesaccordingly. When the thrust acting on the belt increases, a greatfrictional resistance is generated between the clamp surfaces of thesheaves and the contact surfaces of the belt, and an amount of heatgeneration of the belt increases. The heat generation of the beltindicates that kinetic energy is converted into thermal energy. Thetransmission efficiency of torque decreases by a degree corresponding tothe conversion from kinetic energy to thermal energy.

FIG. 19 shows transition of an amount of heat generation of the belt andtransmission efficiency at the time when the thrust acting on the beltis varied. As it is evident from FIG. 19, if the thrust increases, theamount of heat generation of the belt increases in proportion to theincrease in the thrust, and the transmission efficiency of torquedecreases. Therefore, it is necessary to set the thrust to a necessaryminimum level in order to increase the transmission efficiency of torquebetween the sheaves and the belt.

On the other hand, in the belt-type continuously variable transmission,the clamp surfaces of the respective sheaves are subjected to machiningsuch as cutting and grinding. This kind of machining is performed whilethe sheave is being rotated. Therefore, a large number of annulargrooves along a peripheral direction are formed on the clamp surfaces ofthe sheaves. The grooves are very fine with width and depth of aboutseveral μm.

Incidentally, according to the conventional belt-type continuouslyvariable transmission, when driving is started in a newly assembledstate, slip tends to occur in the belt, in particular, at the initialstage of driving. FIG. 20 shows transition of transmission torque of thebelt at the initial stage of driving. As it is evident from FIG. 20, thetorque transmitted to the belt is significantly lower than apredetermined set value C immediately after driving is started. A valueof this torque tends to gradually increase as driving time elapses.After certain time elapses, the torque reaches the set value.

It is assumed that this phenomenon occurs because of the grooves presenton the clamp surfaces of the sheaves in a brand new state. In short, itappears that the presence of the grooves makes a contact state betweenthe sheaves and the belt unstable, causing the slip of the belt.

Therefore, in driving the new belt-type continuously variabletransmission, trial-run of the continuously variable transmission needsto be performed until the torque transmitted to the belt reaches the setvalue. By performing the trial-run, the contact surfaces of the belt areabraded by edges of the grooves of the sheaves and sharp edges of thegrooves are worn. Consequently, the grooves of the sheave are filledwith abrasion waste and the clamp surfaces of the sheaves are smoothed.As a result, the state of contact between the sheaves and the belt isstabilized and the slip of the belt is controlled. As shown in FIG. 20,desired transmission torque is obtained when predetermined trial-run iscompleted.

In the conventional belt-type continuously variable transmission,however, the trial-run needs to be continued until the slip of the beltis completely eliminated. Consequently, long time is required until thecontinuously variable transmission is set in a drivable state and agreat deal of labor is required for shipment of the product, causing anincrease in cost.

As means for controlling slip of the belt at the initial stage ofdriving, it is conceivable to increase the thrust acting on the belt.However, if the thrust is increased, the amount of heat generation ofthe belt inevitably increases as described above. Therefore, after thecompletion of the trial-run, the thrust acting on the belt becomesexcessively large and the transmission efficiency of the torque isdeteriorated.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide a belt-type continuouslyvariable transmission that can prevent slip of a belt while controllingthrust acting on the belt to a necessary minimum necessary level.

It is another object of the invention to provide a sheave for acontinuously variable transmission that can prevent slip of a belt whilecontrolling thrust acting on the belt to a necessary minimum necessarylevel.

It is still another object of the invention to provide a belt for acontinuously variable transmission that can prevent slip on a sheave andcan transmit torque with high efficiency.

It is still another object of the invention to provide a vehicle mountedwith a belt-type continuously variable transmission that can preventslip of a belt while controlling thrust acting on the belt to anecessary minimum necessary level.

In order to achieve the objects, a belt-type continuously variabletransmission according to an aspect of the invention includes:

a primary sheave including a pair of first clamp surfaces that areopposed to each other and a first belt groove formed between the firstclamp surfaces, the primary sheave being capable of adjusting width ofthe first belt groove;

a secondary sheave including a pair of second clamp surfaces opposed toeach other and a second belt groove formed between the second clampsurfaces, the secondary sheave being capable of adjusting width of thesecond belt grooves; and

a belt endlessly wound between the first belt groove of the primarysheave and the second belt groove of the secondary sheave, the belthaving contact surfaces clamped between the first clamp surfaces andbetween the second clamp surfaces, characterized in that

-   -   powder having infusibility as a friction enhancing material is        held on at least one of the first clamp surfaces of the primary        sheave, the second clamp surfaces of the secondary sheave, and        the contact surfaces of the belt.

In order to achieve the objects, a sheave for a continuously variabletransmission according to an aspect of the invention, is characterizedin that friction layers including infusible powder are stacked on a pairof clamp surfaces that clamp a belt.

In order to achieve the objects, a belt for a continuously variabletransmission according to an aspect of the invention is characterized inthat friction layers including infusible powder are stacked on contactsurfaces clamped by a primary sheave and a secondary sheave.

In order to achieve the objects, a vehicle according to an aspect of theinvention is mounted with a belt-type continuously variabletransmission, characterized in that the belt-type continuously variabletransmission includes:

a primary sheave including a pair of first clamp surfaces opposed toeach other and a first belt groove formed between the first clampsurfaces, the primary sheave being capable of adjusting width of thefirst belt groove;

a secondary sheave including a pair of second clamp surfaces opposed toeach other and a second belt groove formed between the second clampsurfaces, the secondary sheave being capable of adjusting width of thesecond belt groove; and

a belt endlessly wound between the first belt groove of the primarysheave and the second belt groove of the secondary sheave, the belthaving contact surfaces clamped between the first clamp surfaces andbetween the second clamp surfaces and transmitting torque of the primarysheave to the secondary sheave, and

powder having infusibility as a friction enhancing material is held onat least one of the first clamp surfaces of the primary sheave, thesecond clamp surfaces of the secondary sheave, and the contact surfacesof the belt.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a motorcycle according to a first embodiment ofthe invention that is mounted with a belt-type continuously variabletransmission;

FIG. 2 is a side view of a power unit according to the first embodimentof the invention that includes a four-cycle engine and the belt-typecontinuously variable transmission:

FIG. 3 is a sectional view of the belt-type continuously variabletransmission according to the first embodiment of the invention;

FIG. 4 is a side view of a belt used in the belt-type continuouslyvariable transmission according to the first embodiment of theinvention;

FIG. 5 is a sectional view of the belt used in the belt-typecontinuously variable transmission according to the first embodiment ofthe invention;

FIG. 6 is a sectional view along line F6-F6 in FIG. 5;

FIG. 7 is a sectional view schematically showing a state in which afriction layer is stacked on a clamp surface of a primary sheave in thefirst embodiment of the invention;

FIG. 8 is a sectional view schematically showing a state in whichinfusible powder is held on the clamp surface of the primary sheave;

FIG. 9 is a sectional view schematically showing a state in whichinfusible powder is interposed between the clamp surface of the primarysheave and a contact surface of the belt;

FIG. 10 is a sectional view showing part A in FIG. 8 in an enlargedscale;

FIG. 11 is a sectional view schematically showing a state in whichinfusible powder is held on the contact surface of the belt in the firstembodiment of the invention;

FIG. 12 is a characteristic chart showing transition of transmissiontorque of the belt with respect to driving time in the first embodimentof the invention;

FIG. 13 is a side view of a belt-type continuously variable transmissionaccording to a second embodiment of the invention showing a positionalrelation between a high friction portion of a sheave and a belt at thetime when a transmission gear ratio is maximum;

FIG. 14 is a side view of the belt-type continuously variabletransmission according to the second embodiment of the invention showinga positional relation between the high friction portion of the sheaveand the belt at the time when a transmission gear ratio is minimum;

FIG. 15 is a side view of a primary sheave according to a thirdembodiment of the invention;

FIG. 16 is a sectional view of the primary sheave according to the thirdembodiment of the invention;

FIG. 17 is a sectional view of a belt according to a fourth embodimentof the invention;

FIG. 18 is a characteristic chart showing a relation between thrust andtransmission torque acting on a belt in a conventional belt-typecontinuously variable transmission;

FIG. 19 is a characteristic chart showing a relation between thrustacting on the belt and an amount of heat generation and transmissionefficiency of the belt in the conventional belt-type continuouslyvariable transmission; and

FIG. 20 is a characteristic chart showing transition of transmissiontorque of the belt with respect to driving time in the conventionalbelt-type continuously variable transmission.

BEST MODE FOR CARRYING OUT THE INVENTION

A first embodiment of the invention will be hereinafter explained withreference to FIGS. 1 to 12.

FIG. 1 discloses a motorcycle 1 that is an example of a vehicleaccording to the invention. The motorcycle 1 has a frame 2. The frame 2includes a steering head pipe 3, a pair of main pipes 4 (only one mainpipe 4 is shown) and a pair of seat rails 5 (only one seat rail 5 isshown). The steering head pipe 3 is located at a front end of the frame2 and supports a front wheel 7 via a front fork 6.

Each of the main pipes 4 extends rearwards from the steering head pipe3. The main pipe 4 includes a front-half portion 4 a that extendsobliquely downward from the steering head pipe 3, a rear-half portion 4b that extends obliquely upward from a lower end of the front-halfportion 4 a, and an intermediate portion 4 c that is located between thefront-half portion 4 a and the rear-half portion 4 b.

The seat rail 5 is suspended between the front-half portion 4 a and therear-half portion 4 b of the main pipe 4. The seat rail 5 supports aseat 8 over which a rider straddles. The frame 2 is covered with a bodycover 9. The body cover 9 continues to the lower end of the seat 8.

A rear arm bracket 10 is fixed to the intermediate portion 4 c of eachof the main pipes 4. The rear arm bracket 10 projects downward from theintermediate portion 4 c of the main pipe 4. The rear arm bracket 10supports a rear arm 11 that extends rearward. The rear arm 11 isvertically swingable relative to the frame 2. A rear end of the rear arm11 supports a rear wheel 12 as a running body.

The frame 2 supports a power unit 13 that drives the rear wheel 12. Asshown in FIGS. 1 and 2, the power unit 13 includes a four-cyclesingle-cylinder engine 14 as a drive source and a belt-type continuouslyvariable transmission 15. This power unit 13 is covered with a lowerpart of the body cover 9.

The engine 14 is suspended at the front-half portion 4 a of the mainpipe 4. The engine 14 includes a crank case 16 and a cylinder 17 coupledto the crank case 16.

The crank case 16 contains a crank shaft 18 and a not shown gearreduction unit. As shown in FIG. 3, the crank shaft 18 is supported bythe crank case 16 via bearings 19 a and 19 b. The crank shaft 18 ishorizontally arranged in a width direction of the motorcycle 1.

The gear reduction unit has a drive sprocket 20 (shown in FIG. 1) at anoutput end thereof. The drive sprocket 20 is located behind the crankshaft 18. A chain 22 is wound between the drive sprocket 20 and a drivensprocket 21 of the rear wheel 12.

The cylinder 17 of the engine 14 projects upward from the crank case 16along the front-half portion 4 a of the main pipe 4. The cylinder 17contains a piston 23. The piston 23 is coupled to crank webs 25 a and 25b of the crank shaft 18 via a connecting rod 24.

As shown in FIGS. 2 and 3, the belt-type continuously variabletransmission (hereinafter referred to as “CVT”) 15 is located on theright side of the crank case 16. The CVT 15 is contained in atransmission case 28. The transmission case 28 is fixed to the rightside surface of the crank case 16.

The CVT 15 includes a primary sheave 29, a secondary sheave 30, and abelt 31. The primary sheave 29 is located at a front end of thetransmission case 28 and supported by an input shaft 32. The input shaft32 is integrated with the crank shaft 18. In other words, a journalsection 18 a located at the right end of the crank shaft 18 is extendedtoward the front end of the transmission case 28 and this extended partalso serves as the input shaft 32.

The primary sheave 29 includes a fixed plate 34 a and a sliding plate 34b. The fixed plate 34 a is fixed to a shaft end of the input shaft 32and rotates together with the input shaft 32. The sliding plate 34 b hasa cylindrical boss portion 35. The boss portion 35 is supported on theinput shaft 32 via a collar 36. Thus, the sliding plate 34 b is slidablein directions the sliding plate 34 b approaches and moves away from thefixed plate 34 a. The sliding plate 34 b is rotatable in a peripheraldirection of the input shaft 32.

The primary sheave 29 has a pair of first clamp surfaces 37 a and 37 b.One first clamp surface 37 a is formed on the fixed plate 34 a. Theother first clamp surface 37 b is formed on the sliding plate 34 b. Thefirst clamp surfaces 37 a and 37 b have a conical shape and are opposedto each other. The first clamp surfaces 37 a and 37 b define a firstbelt groove 38 having a V-sectional shape between the fixed plate 34 aand the sliding plate 34 b. Width L1 of the first belt groove 38 isadjusted by sliding movement of the sliding plate 34 b.

A cam plate 39 is fixed to an outer periphery of the input shaft 32. Thecam plate 39 rotates together with the input shaft 32 and is opposed tothe sliding plate 34 b. The sliding plate 34 b is hooked on the camplate 39 so as to be slidable in the axial direction of the input shaft32. Accordingly, the cam plate 39 and the sliding plate 34 b are movablein directions in which the cam plate 39 and the sliding plate 34 bapproach and move away from each other while rotating together.

The sliding plate 34 b has a cam surface 40 that is opposed to the camplate 39. Plural roller weights 41 (only one roller weight is shown) areinterposed between the cam surface 40 and the cam plate 39. The rollerweight 41 moves along the cam surface 40 with centrifugal force that isgenerated when the crank shaft 18 rotates. According to the movement,the sliding plate 34 b slides in the axial direction of the input shaft32 and the width L1 of the first belt groove 38 changes.

The secondary sheave 30 is located at a rear end of the transmissioncase 28 and is supported on an output shaft 42. The output shaft 42 isarranged in parallel to the input shaft 32 and coupled to an input endof the gear reduction unit via a not shown automatic centrifugal clutch.

The secondary sheave 30 includes a fixed plate 45 a and a sliding plate45 b. The fixed plate 45 a has a cylindrical collar 46 at a rotationalcenter thereof. The collar 46 meshes with the outer peripheral surfaceof the output shaft 42. According to this meshing, the fixed plate 45 aand the output shaft 42 rotate together.

The sliding plate 45 b has a sleeve 47 at a rotational center thereof.The sleeve 47 is provided on the outer peripheral surface of the collar46 so as to be slidable in the axial direction. Plural engagementgrooves 48 are formed in the sleeve 47. The engagement grooves 48 extendin the axial direction of the sleeve 47 and are arranged in theperipheral direction of the sleeve 47 at intervals.

The collar 46 has plural engaging pins 49. The engaging pins 49 projectto the outside of the collar 46 and are slidably fitted in theengagement grooves 48 of the sleeve 47. Consequently, the fixed plate 45a and the sliding plate 45 b are movable in directions in which thefixed plate 45 a and the sliding plate 45 b approach and move away fromeach other while rotating together.

The secondary sheave 30 has a pair of second clamp surfaces 51 a and 51b. One second clamp surface 51 a is formed on the fixed plate 45 a. Theother second clamp surface 51 b is formed on the sliding plate 45 b. Thesecond clamp surfaces 51 a and 51 b are formed in a conical shape andare opposed to each other. The second clamp surfaces 51 a and 51 bdefine a second belt groove 52 having a V-sectional shape between thefixed plate 45 a and the sliding plate 45 b. Width L2 of the second beltgroove 52 is adjustable according to sliding movement of the slidingplate 45 b.

A spring seat 53 is secured to an end of the collar 46. The spring seat53 is opposed to the sliding plate 45 b. A compression coil spring 54 isinterposed between the spring seat 53 and the sliding plate 45 b. Thespring 54 biases the sliding plate 45 b toward the fixed plate 45 a.

As shown in FIG. 3, the belt 31 is endlessly wound between the firstbelt groove 38 of the primary sheave 29 and the second belt groove 52 ofthe secondary sheave 30. As shown in FIGS. 4 to 6, the belt 31 includesa plurality of resin blocks 56 and a pair of coupling members 57.

Polyamide resin is used for the resin blocks 56 as a matrix. Carbonfibers or aramid fibers are mixed in the matrix as reinforcementmaterial. The polyamide resin has a high heat resistance and isresistive to a repeated impact load. The polyamide resin can maintain astable quality over a long time period. The carbon fibers and aramidfibers have both high strength and heat resistance. Therefore, the resinblocks 56 are excellent in heat resistance, wear resistance, and fatigueresistance.

As shown in FIG. 5, each of the resin blocks 56 has a pair of contactsurfaces 58 a and 58 b. The contact surfaces 58 a and 58 b are locatedapart from each other in the width direction of the belt 31. The contactsurfaces 58 a and 58 b are inclined so as to extend along the firstclamp surfaces 37 a and 37 b of the primary sheave 29 and the secondclamp surfaces 51 a and 51 b of the secondary sheave 30, respectively.Recesses 59 are formed in central parts of the contact surfaces 58 a and58 b of each of the resin blocks 56 respectively.

The coupling members 57 are formed of, for example, refractory rubber.Plural core wires 60 for reinforcement are buried in the couplingmembers 57. The coupling members 57 have an annular shape and are fittedin the recesses 59 of the resin block 56. Through this fitting, theresin blocks 56 are coupled to one another to constitute the endlessbelt 31.

The coupling member 57 fitted in the recesses 59 retracts from thecontact surfaces 58 a and 58 b of the resin blocks 56. Therefore, whenthe belt 31 is wound around the first and the second belt grooves 38 and52, only the contact surfaces 58 a and 58 b of the resin blocks 56 comeinto contact with the first clamp surfaces 37 a and 37 b of the primarysheave 29 and the second clamp surfaces 51 a and 51 b of the secondarysheave 30.

In other words, the first clamp surfaces 37 a and 37 b of the primarysheave 29 and the second clamp surfaces 51 a and 51 b of the secondarysheave 30 clamp the resin blocks 56 of the belt 31 with predeterminedthrust. Consequently, desired transmission torque is obtained betweenthe primary sheave 29 and the belt 31 and between the secondary sheave30 and the belt 31.

In a state in which the rotation speed of the crank shaft 18 is low, forexample, at the time the engine 14 is idling, the roller weights 41 areshifted to a rotational center of the primary sheave 29. Therefore, thesliding plate 34 b is located in a position farthest from the fixedplate 34 a and the width L1 of the first belt groove 38 is maximized.Consequently, the belt 31 wound around the first belt groove 38 islocated at the rotational center of the primary sheave 29. A diameter ofthe belt 31 wound around the primary sheave 29 is minimized.

On the other hand, in the secondary sheave 30, the sliding plate 45 b isbiased toward the fixed plate 45 a by the spring 54. The width L2 of thesecond belt groove 52 is minimized. Consequently, the belt 31 woundaround the second belt groove 52 is pushed out to an outer periphery ofthe secondary sheave 30. A diameter of the belt 31 wound around thesecondary sheave 30 is maximized. Therefore, the CVT 15 has a maximumtransmission gear ratio.

As the number of revolutions of the crank shaft 18 increases, the rollerweights 41 move outward in a radial direction of the sliding plate 34 bwith the centrifugal force. According to this movement, the slidingplate 34 b slides toward the fixed plate 34 a and the width L1 of thefirst belt groove 38 gradually decreases. As a result, the belt 31clamped between the first clamp surfaces 37 a and 37 b is pushed outwardin a radial direction of the primary sheave 29. A diameter of the belt31 wound around the primary sheave 29 increases.

Conversely, in the secondary sheave 30, the belt 31 is pulled toward therotational center of the secondary sheave 30. Consequently, the slidingplate 45 b slides in a direction in which the sliding plate 45 b movesaway from the fixed plate 45 a against the biasing force of the spring54. The width L2 of the second belt groove 38 gradually increases.Therefore, a diameter of the belt 31 wound around the secondary sheave30 decreases. Thus, the transmission gear ratio of the CVT 15 decreases.The transmission gear ratio of the CVT 15 is minimized when a diameterof the belt 31 wound around the primary sheave 29 is maximized.

The fixed plate 34 a of the primary sheave 29 and the fixed plate 45 aof the secondary sheave 30 are formed of, for example,chromium-molybdenum steel (SCM420) subjected to carburizing, quenching,and tempering treatment. The fixed plates 34 a and 45 a have surfacehardness indicated by 80±2 HRA. The sliding plate 34 b of the primarysheave 29 is formed of a die-cast aluminum alloy (YDC11) subjected tosurface treatment such as chrome plating. The sliding plate 34 b hassurface hardness indicated by 800 HV or more. The sliding plate 45 b ofthe secondary sheave 30 is formed of mechanical structure carbon steel(S35C) and has surface hardness indicated by 63 HB.

The first clamp surfaces 37 a and 37 b of the primary sheave 29 and thesecond clamp surfaces 51 a and 51 b of the secondary sheave 30 arefinished in a predetermined shape by machining such as cutting orgrinding. Consequently, as represented by the first clamp surface 37 aof the primary sheave 29 in FIG. 7, the first clamp surface 37 a has alarge number of grooves 62 formed by machining. The grooves 62 are veryfine with width and depth of about several μm. The grooves 62 are a kindof recess.

The first clamp surfaces 37 a and 37 b of the primary sheave 29 and eachof the second clamp surfaces 51 a and 51 b of the secondary sheave 30are covered with friction layers 63 entirely, respectively. The frictionlayers 63 are obtained by coating, for example, carbon powder 64, whichis a friction enhancing material, on the first clamp surfaces 37 a and37 b and the second clamp surfaces 51 a and 51 b, for which machininghas been completed. As represented by the first clamping surface 37 a ofthe primary sheave 29 in FIG. 7, the friction layer 63 is stacked on thefirst clamp surface 37 a so as to have thickness enough for burying thegrooves 62 sufficiently.

The friction layers 63 do not always have to cover the entire first andsecond clamp surfaces 37 a, 37 b, 51 a, and 51 b. For example, in thefirst and the second clamp surfaces 37 a, 37 b, 51 a, and 51 b, onlyregions in contact with the belt 31 may be covered with the frictionlayers 63. In addition, in the first and the second clamp surfaces 37 a,37 b, 51 a, and 51 b, only regions, which clamp the belt 31 when the CVT15 has a maximum transmission gear ratio, may be covered with thefriction layers 63.

The carbon powder 64 has infusibility. The carbon powder 64 has such acharacteristic as to withstand the heat and pressure that are generatedduring the speed change operation of the CVT 15. More specifically, whenthe belt 31 is clamped between the first clamp surfaces 37 a and 37 b ofthe primary sheave 29 and between the second clamp surfaces 51 a and 51b of the secondary sheave 30, heat due to friction is generated incontact parts between the contact surfaces 58 a and 58 b of the belt 31and the first and the second clamp surfaces 37 a, 37 b, 51 a, and 51 b.Consequently, since the carbon powder 31 has such a characteristic thatcarbon powder is not fused by the heat in the contact parts, the carbonpowder 31 can maintain the powder state.

In addition, the carbon powder 64 has hardness lower than that of thefirst clamp surfaces 37 a and 37 b of the primary sheave 29 and thesecond clamp surfaces 51 a and 51 b of the secondary sheave 30.

In the new CVT 15 that has just been assembled, the first clamp surfaces37 a and 37 b of the primary sheave 29 and the second clamp surfaces 51a and 51 b of the secondary sheave 30 are covered with the frictionlayers 63. Consequently, the carbon powder 64 is in a state in which thecarbon powder 64 is held on the first and the second clamp surfaces 37a, 37 b, 51 a, and 51 b.

If the driving of the new CVT 15 is started, as represented by theprimary sheave 29 in FIG. 9, the carbon powder 64 enters a slight gap gbetween the primary sheave 29 and the belt 31 at the initial stage ofdriving. Consequently, a contact area of the primary sheave 29 and thebelt 31 and a contact area of the secondary shave 30 and the belt 31increase. The carbon powder 64 has infusibility in that the carbonpowder 64 maintains the powder state even if heat is applied during thespeed change operation. Therefore, the carbon powder 64 functions as aslip-stopper for the belt 31.

FIGS. 8 and 10 disclose a state of the first clamp surface 37 a at thetime when the driving of the CVT 15 is continues. Since the other firstclamp surface 37 b and the second clamp surfaces 51 a and 51 b have thesame state as that of the first clamp surface 37 a, the first clampsurfaces 37 a is described here as a representative.

As driving time elapses, a part of the friction layer 63 covering thefirst clamp surface 37 a is removed from the first clamp surface 37 a bythe contact with the belt 31 and dispersed into the transmission case28. Consequently, the carbon powder 64, which enters into the grooves62, remains on the first clamp surface 37 a. At the same time, edges ofthe grooves 62 are scraped off by the contact with the belt 31,resulting in a decrease in depth of the grooves 62.

On the other hand, in the belt 31, the contact surfaces 58 a and 58 b ofresin blocks 56 are scraped off by the contact with the first clampsurface 37 a. Consequently, initial wear of the belt 31 occurs. As shownin FIG. 10, a scraped resin component 65 of the belt 31 is transferredto the groove 62 and cooperates with the carbon powder 64 to fill thegroove 62. The first clamp surface 37 a is smoothed.

As shown in FIG. 11, the carbon powder 64 adheres to the contact surface58 a of the resin block 56. The carbon powder 64 fills uneven portionson the contact surface 58 a, thereby smoothing the contact surface 58 a.Therefore, the contact state between the contact surface 58 a of thebelt 31 and the first clamp surface 37 a of the primary sheave 29 isstabilized.

According to such a first embodiment of the invention, at the initialstage of driving of the CVT 15, the carbon powder 64 prevents slip ofthe belt 31. Consequently, without increasing thrust for clamping thebelt 31, it is possible to improve torque transmission efficiencybetween the primary sheave 29 and the belt 31 and between the secondarysheave 30 and the belt 31 at the beginning of driving. This makestrial-run unnecessary.

After fixed time elapses from the beginning of driving, the frictionlayer 63 is removed and the residual carbon powder 64 fills the grooves62 of the first clamp surface 37 a. Consequently, the slip preventionfunction of the carbon powder 64 is lost. The transmission torquechanges to a value corresponding to the thrust between the primarysheave 29 and the belt 31 and between the secondary sheave 30 and thebelt 31.

FIG. 12 discloses transition of transmission torque following elapse ofdriving time at the initial stage of driving in CVT 15 of thisembodiment. As shown in FIG. 12, a value of transmission torque A at theinitial stage of driving is slightly higher than a predeterminedoriginal value of transmission torque B because of the presence of thecarbon powder 64. This value of the transmission torque A graduallydecreases as time elapses and finally coincides with a value of normaltransmission torque B. The reason appears to be that the friction layer63 is removed by the contact with the belt 31 and the slip preventionfunction of the carbon powder 64 at the initial stage of driving islost.

According to the above-described structure, the carbon powder 64 hashardness lower than that of the first clamp surfaces 37 a and 37 b ofthe primary sheave 29 and the second clamp surfaces 51 a and 51 b of thesecondary sheave 30. Consequently, the carbon powder 64 never damagesthe first clamp surfaces 37 a and 37 b or the second clamp surfaces 51 aand 51 b. Therefore, it is possible to control wear of the first clampsurfaces 37 a and 37 b or the second clamp surfaces 51 a and 51 balthough the structure, which the slip of the belt 31 can be prevented.

Moreover, according to this embodiment, the plural resin blocks 56constituting the belt 31 are formed of polyamide resin. Thus, the heatresistance and durability of the belt 31 are improved and stableperformance of the belt 31 can be maintained over a long time period.

FIGS. 13 and 14 disclose a second embodiment of the invention. Thesecond embodiment differs from the first embodiment in the first clampsurfaces 37 a and 37 b of the primary sheave 29 and the second clampsurfaces 51 a and 51 b of the secondary sheave 30. The other componentsof the CVT 15 in the second embodiment are the same as those in thefirst embodiment. Consequently, in the second embodiment, the componentssame as those in the first embodiment are denoted by like referencenumerals and explanations of the components are omitted.

The first clamp surfaces 37 a and 37 b of the primary sheave 29 havehigh friction portions 71. Similarly, the second clamp surfaces 51 a and51 b of the secondary sheave 30 have high friction portions 72. The highfriction portions 71 and 72 are obtained by subjecting the first clampsurfaces 37 a and 37 b and the second clamp surfaces 51 a and 51 b toshot peening or honing respectively. The high friction portions 71 and72 include a large number of fine uneven portions. The uneven portionsare formed to have a net-like pattern with no orientation.

The high friction portions 71 of the primary sheave 29 are annularlyformed at the rotational center of the first clamp surfaces 37 a and 37b. Consequently, when a diameter of the belt 31 wound around the primarysheave 29 is minimized, the belt 31 is clamped between the high frictionportions 71. Portions of the first clamp surfaces 37 a and 37 b out ofthe high friction portions 71 are machined surface portions 73 subjectedto machining such as cutting or grinding. The high friction portions 70have a friction coefficient higher than that of the machined surfaceportion 73.

The high friction portions 72 of the secondary sheave 30 are annularlyformed at the outer periphery of the second clamp surfaces 51 a and 51b. Consequently, when a diameter of the belt 31 wound around thesecondary sheave 30 is maximized, the belt 31 is clamped between thehigh friction portions 72. Portions of the second clamp surfaces 51 aand 51 b out of the high friction portions 72 are machined surfaceportions 74 subjected to machining such as cutting or grinding. The highfriction portions 72 have a friction coefficient higher than that of themachined surface portions 74.

Although not shown, the first clamp surfaces 37 a and 37 b and thesecond clamp surfaces 51 a and 51 b are covered with the same frictionlayers as in the first embodiment. The friction layers are stacked onthe first clamp surfaces 37 a and 37 b and the second clamp surfaces 51a and 51 b to thickness enough for filling the grooves formed bymachining and the uneven portions of the high friction portions 71 and72.

According to such a structure, the belt 31 is clamped between the highfriction portions 71 of the primary sheave 29 and the high frictionportions 72 of the secondary sheave 30 in such a driving state that adiameter of the belt 31 wound around the primary sheave 29 is minimizedand a diameter of the belt 31 wound around the secondary sheave 30 ismaximized. In other words, in such a driving state that the transmissiongear ratio of the CVT 15 is maximized, the belt 31 is clamped betweenportions of the first clamp surfaces 37 a and 37 b and the second clampsurfaces 51 a and 51 b having high friction coefficients.

Consequently, at the initial stage of driving, the carbon powder 64tends to stop between the primary sheave 29 and the belt 31 and betweenthe secondary sheave 30 and the belt 31. Thus, slip of the belt 31 canbe surely prevented in such a driving state that the transmission gearratio of the CVT 15 is maximized and the tension acting on the belt 31is maximized.

According to the structure described above, as the transmission gearratio of the CVT 15 gradually decreases, the belt 31 moves out of thehigh friction portions 71 and 72. Therefore, it is possible to preventwear of the belt 31 in such a driving state that the tension acting onthe belt 31 decreases.

The high friction portions 71 and 72 only have to be formed on a part ofthe first clamp surfaces 37 a and 37 b and the second clamp surfaces 51a and 51 b. A range of machining for obtaining the high frictionportions 71 and 72 is small. Accordingly, manufacturing cost of theprimary sheave 29 and the secondary sheave 30 can be reduced.

FIGS. 15 and 16 disclose a third embodiment of the invention.

In the third embodiment, the fixed plate 34 a of the primary sheave 29is described as an example. As shown in FIG. 15, plural rib-likeprojections 81 are formed on the first clamp surface 37 a of the fixedplate 34 a. The projections 81 extend radially from the rotationalcenter of the fixed plate 34 a over the entire first clamp surface 37 a.The projections 81 define plural radial grooves 82 over the first clampsurface 37 a. The projections 81 and the grooves 82 are alternatelyarranged on the first clamp surface 37 a. Consequently, the entire firstclamp surface 37 a functions as a high friction portion 83 with a highfriction coefficient.

Although not shown, the first clamp surface 37 a is coated with the samefriction layer as in the first embodiment. The friction layer is stackedon the first clamp surface 37 a to thickness sufficient for filling theprojections 81 and the grooves 82.

According to this structure, since the high friction portion 83 islocated over the entire first clamp surface 37 a, the carbon powder issurely held on the first clamp surface 37 a. Even if the position of thewound belt 31 changes, slip of the belt 31 can be prevented.

FIG. 17 discloses a fourth embodiment of the invention.

In the fourth embodiment, the contact surfaces 58 a and 58 b of the belt31 are covered with friction layers 63 which increases the friction. Thestructure of the belt 31 is the same as that in the first embodiment. Inaddition, as in the first embodiment, the friction layers 63 containinfusible carbon powder.

According to the fourth embodiment, the friction layers 63 are stackedon the contact surfaces 58 a and 58 b of the belt 31 to thicknesssufficient for filling the uneven portions of the contact surfaces 58 aand 58 b of the belt 31.

When the new belt 31 is wound between the primary sheave and thesecondary sheave, the friction layers 63 are interposed between the belt31 and both the sheaves. In the initial stage of driving, the carbonpowder contained in the friction layers 63 enters slight gaps betweenthe belt 31 and both the sheaves. Consequently, contact areas betweenthe belt 31 and the respective sheaves increase. As a result, as in thefirst embodiment, the carbon powder functions as a slip-stopper for thebelt 31.

In the first embodiment, the carbon powder 64 is used as a slip-stopperfor the belt 31. However, the invention is not limited to thisembodiment. Other kinds of powder such as carbon black may be used.

Specifically, graphite powder, which is a kind of carbon black, isusable. It is preferable to use graphite powder with a grain size of 5μm to 150 μm. When graphite powder is used to form a friction layer,first, a liquid-phase material obtained by mixing graphite powder with abinder and a diluent is prepared. The liquid-phase material is appliedto at least one of a primary sheave, a secondary sheave, and a belt.

The binder is resin for fixing the graphite powder to the primarysheave, the secondary sheave, or the belt. As this resin, acrylic resinor olefin resin is suitable taking into account drying time and loadingsof the liquid-phase material. The diluent keeps viscosity of theliquid-phase material properly to make it easy to adjust density andthickness of the friction layer and improve work efficiency in applyingthe liquid-phase material. Examples of the diluent include an estersolvent represented by butyl acetate, a ketone solvent represented bymethyl ethyl ketone, a petroleum solvent represented by hexane, and analcohol solvent represented by methyl alcohol.

It is desirable that a compounding ratio of the graphite powder, thebinder, and the diluent is set to 2 to 80 wt % for the graphite powderand the remaining 20 to 98 wt % for the binder and the diluent.

It is possible to use powdery zinc oxide or particulate silica powderfor stopping slip of the belt 31. However, the carbon powder isinexpensive compared with zinc oxide and is advantageous in terms ofcost. Besides, the carbon powder has low hardness compared with silicaand does not easily damage the sheave. Thus, taking into account costand an effect on sheaves, it is desirable to use the carbon powder.

In the first embodiment, friction layers are formed on both the primarysheave and the secondary sheave. However, the invention is not limitedto this. Friction layers may be formed on one of the primary sheave andthe secondary sheave. According to this constitution, powder containedin the friction layers is fed to the other sheave, which has no frictionlayer, via the belt. Therefore, it is possible to prevent slip betweenboth the sheaves and the belt.

When the present invention is carried out, friction layers may be formedon all of the primary sheave, the secondary sheave, and the belt.

The vehicle according to the invention is not limited to a motorcycle.The invention is similarly applicable to, for example, an ATV(All-Terrain Vehicle) with three or four wheels for running on roughgrounds or to a snowmobile.

INDUSTRIAL APPLICABILITY

According to the invention, the infusible powder prevents slip of thebelt at the initial stage of driving. Consequently, without increasingthe thrust for clamping the belt, the torque transmission efficiency canbe improved between the primary sheave and the belt and between thesecondary sheave and the belt. Therefore, a desired transmission torquecan be obtained from the beginning of driving and trial-run is madeunnecessary.

1. A belt-type continuously variable transmission, characterized bycomprising: a primary sheave including a pair of first clamp surfacesopposed to each other and a first belt groove formed between the firstclamp surfaces, the primary sheave being capable of adjusting width ofthe first belt groove; a secondary sheave including a pair of secondclamp surfaces opposed to each other and a second belt groove formedbetween the second clamp surfaces, the secondary sheave being capable ofadjusting width of the second belt groove; and a belt endlessly woundbetween the first belt groove of the primary sheave and the second beltgroove of the secondary sheave, the belt having contact surfaces thatare clamped between the first clamp surfaces and between the secondclamp surfaces, torque of the primary sheave being transmitted to thesecondary sheave via the belt, and in that powder having infusibility asa friction enhancing material is held on at least one of the first clampsurfaces of the primary sheave, the second clamp surfaces of thesecondary sheave, and the contact surfaces of the belt.
 2. A belt-typecontinuously variable transmission according to claim 1, characterizedin that the first clamp surfaces of the primary sheave and the secondclamp surfaces of the secondary sheave have plural recesses that holdthe powder.
 3. A belt-type continuously variable transmission accordingto claim 1, characterized in that the contact surfaces of the belt haveplural recesses that hold the powder.
 4. A belt-type continuouslyvariable transmission according to any one of claims 1 to 3,characterized in that the powder is powder of one of carbon, zinc oxide,and silica.
 5. A belt-type continuously variable transmission accordingto claim 1, characterized in that the powder has such a characteristicthat, when the belt is clamped between the first clamp surfaces andbetween the second clamp surfaces, the powder is not fused by heat thatis generated by friction between the contact surfaces of the belt andthe first and the second clamp surfaces.
 6. A belt-type continuouslyvariable transmission according to claim 1, characterized in that thepowder has hardness lower than that of the first clamp surfaces of theprimary sheave and the second clamp surfaces of the secondary sheave. 7.A belt-type continuously variable transmission according to claim 1,characterized in that the belt includes plural resin blocks havingcontact surfaces and a coupling member that endlessly couples the resinblocks.
 8. A belt-type continuously variable transmission according toclaim 7, characterized in that polyamide resin is used as a matrix ofthe resin blocks, and a reinforcement material of carbon fibers oraramid fibers are mixed in the matrix.
 9. A belt-type continuouslyvariable transmission, characterized by comprising: a primary sheaveincluding a pair of first clamp surfaces opposed to each other and afirst belt groove formed between the first clamp surfaces, the primarysheave being capable of adjusting width of the first belt groove; asecondary sheave including a pair of second clamp surfaces opposed toeach other and a second belt groove formed between the second clampsurfaces, the secondary sheave being capable of adjusting width of thesecond belt groove; and a belt endlessly wound between the first beltgroove of the primary sheave and the second belt groove of the secondarysheave, the belt having contact surfaces clamped between the first clampsurfaces and between the second clamp surfaces, torque of the primarysheave being transmitted to the secondary sheave via the belt, and inthat friction layers including infusible powder are stacked on at leastone of the first clamp surfaces of the primary sheave, the second clampsurfaces of the secondary sheave, and the contact surfaces of the belt.10. A belt-type continuously variable transmission according to claim 9,characterized in that the first clamp surfaces of the primary sheave andthe second clamp surfaces of the secondary sheave have plural recessesthat hold the powder.
 11. A belt-type continuously variable transmissionaccording to claim 10, characterized in that the contact surfaces of thebelt have plural recesses that hold the powder.
 12. A belt-typecontinuously variable transmission according to claim 9, characterizedin that the powder has such a characteristic that, when the belt isclamped between the first clamp surfaces and between the second clampsurfaces, the powder is not fused by heat that is generated by frictionbetween the contact surfaces of the belt and the first and the secondclamp surfaces.
 13. A belt-type continuously variable transmissionaccording to any one of claims 9 to 12, characterized in that thefriction layers are formed by applying one of carbon, zinc oxide, andsilica to at least one of the first clamp surfaces of the primarysheave, the second clamp surfaces of the secondary sheave, and thecontact surfaces of the belt.
 14. A belt-type continuously variabletransmission according to any one of claims 9 to 12, characterized inthat the friction layers are formed by applying a material, which isobtained by mixing a binder in carbon black powder, to at least one ofthe first clamp surfaces of the primary sheave, the second clampsurfaces of the secondary sheave, and the contact surfaces of the belt.15. A belt-type continuously variable transmission according to claim 9,characterized in that, when predetermined driving time elapses, at leasta part of the friction layers are removed, and a residual part of thepowder included in the friction layers is held on at least one of thefirst clamp surfaces of the primary sheave, the second clamp surfaces ofthe secondary sheave, and the contact surfaces of the belt.
 16. Abelt-type continuously variable transmission according to claim 9,characterized in that the belt includes plural resin blocks having thecontact surfaces and a coupling member that endlessly couples the resinblocks, and polyamide resin is used as a matrix of the resin blocks anda reinforcement material of carbon fibers or aramid fibers are mixed inthe matrix.
 17. A sheave for a continuously variable transmission,characterized by comprising a pair of clamp surfaces that clamp a belt,and in that friction layers including infusible powder are stacked onthe clamp surfaces.
 18. A sheave for a continuously variabletransmission according to claim 17, characterized in that the clampsurfaces have plural recesses that hold the powder.
 19. A sheave for acontinuously variable transmission according to claim 17 or 18,characterized in that the friction layers are formed by applying amaterial, which is obtained by mixing a binder in carbon black powder,to the clamp surfaces.
 20. A sheave for a continuously variabletransmission according to claim 17, characterized in that the powder hassuch a characteristic that, when the belt is clamped between the clampsurfaces, the powder is not fused by heat that is generated by frictionbetween the belt and the clamp surfaces.
 21. A sheave for a continuouslyvariable transmission according to claim 17 or 20, characterized in thatthe powder has hardness lower than that of the clamp surfaces.
 22. Abelt for a continuously variable transmission that is endlessly woundbetween a primary sheave and a secondary sheave, the belt havingcontacts surfaces clamped by the respective sheaves and transmittingtorque of the primary sheave to the secondary sheave, characterized inthat: friction layers including infusible powder are stacked on thecontact surfaces.
 23. A belt for a continuously variable transmission,characterized by comprising: plural resin blocks having contact surfacesclamped by a primary sheave made of metal and a secondary sheave made ofmetal; and a coupling member that endlessly couples the resin blocks,the belt being endlessly wound between the primary sheave and thesecondary sheave to thereby transmit torque of the primary sheave to thesecondary sheave, and in that friction layers including infusible powderare stacked on the contact surfaces.
 24. A belt for a continuouslyvariable transmission according to claim 22 or 23, characterized in thatthe friction layers are formed by applying a material, which is obtainedby mixing a binder in carbon black powder, to the contact surfaces. 25.A belt for a continuously variable transmission according to claim 22 or23, characterized in that the powder has such a characteristic that thepowder is not fused by heat that is generated by friction between thecontact surfaces and the primary sheave and the secondary sheave.
 26. Abelt for continuously variable transmission according to claim 22 or 23,characterized in that the contact surfaces have plural recesses thathold the powder.
 27. A vehicle mounted with a belt-type continuouslyvariable transmission, characterized in that the belt-type continuouslyvariable transmission includes: a primary sheave including a pair offirst clamp surfaces opposed to each other and a first belt grooveformed between the first clamp surfaces, the primary sheave beingcapable of adjusting width of the first belt groove; a secondary sheaveincluding a pair of second clamp surfaces opposed to each other and asecond belt groove formed between the second clamp surfaces, thesecondary sheave being capable of adjusting width of the second beltgroove; a belt endlessly wound between the first belt groove of theprimary sheave and the second belt groove of the secondary sheave, thebelt having contact surfaces clamped between the first clamp surfacesand between the second clamp surfaces and transmitting torque of theprimary sheave to the secondary sheave; and powder having infusibilityas a friction enhancing material that is held on at least one of thefirst clamp surfaces of the primary sheave, the second clamp surfaces ofthe secondary sheave, and the contact surfaces of the belt.
 28. Avehicle according to claim 27, characterized in that the primary sheaveis driven by power transmission from a drive source, and the secondarysheave is interlocked with a running body for running.
 29. A vehicleaccording to claim 27, characterized in that the powder has such acharacteristic that, when the belt is clamped between the first clampsurfaces and between the second clamp surfaces, the powder is not fusedby heat that is generated by friction between the contact surfaces ofthe belt and the first and the second clamp surfaces.